Hydraulic rock drill rigs in the past have had a relatively restricted range of movement, thereby substantially limiting the pattern for entry of the long drill rod carrying the drill bit at its outer tip. For example, entry patterns in the vertical plane may be limited to a maximum swing of about 90.degree. and a maximum reach in this plane of about 5 feet. Similarly, the entry pattern for drilling in the horizontal plane may be limited to a range of swing toward the front of the drilling rig so that holes may be drilled only in a forward direction, such as a forward entry pattern falling within a concave rectangle no more than 10 feet high and 30 feet wide.
While it has been proposed in U.S. Pat. No. 4,199,033 to Gundy to provide an augering attachment for a backhoe, the distance that the tip of the auger extends beyond the distal end of the boom is fixed, and the swiveling connection for attaching the auger to the distal end of the boom is not sufficiently sturdy to endure the stresses generated by the pounding of a percussive rock drill. In addition, the boom to which the auger is attached is limited to a pivotal movement toward the rear of the backhoe tractor.